Castelli first introduced Nano Flex arm and leg warmers more than 5 years ago, adding a water repellent feature to the warmers that helps keep your arms or legs drier through misting, sprinkling rain, or road spray. New for 2018, Castelli has updated the construction of the warmers by using a different “Nano Light” fabric on the backs of the knees and bends of the elbows so that they move better with your arms and legs.

Arm warmers and leg or knee warmers come in very handy when you’re on a ride with the changing temperatures that are common in the spring and the fall. If the temperature rises, you can peel them off and put them in your jersey pocket, where they take up very little room. Or carry them along if you think the weather might change and the temperature might drop later.

What I liked about the Nano Flex material is that although it’s fairly effective at keeping water from soaking through, it still mostly feels like a regular arm or leg warmer when you are wearing it. I’d say that it’s slightly less breathable, but not enough that it matters. These could easily be your only set of arm or leg warmers, which would give you the benefits of the water repellency without requiring you to only choose them if you think it might be wet.

I wore these on some early morning, cool weather March rides in the mid to low 40s, and they kept me warm enough. The package rates them to 46 degrees. The weather was dry when I tested them, and I prefer not to ride in the rain when it is cold anyway. I did spray my arms and legs with a water bottle to see how they worked, and they are effective. They aren’t intended to keep you 100 percent dry, but they repel a lot of water. You can see it bead up on the outside of the warmers.

The knee warmers were fairly long and came down a little more than halfway down my calves, sort of like a 3/4 length pair of winter knicker style of cycling shorts. The leg warmers were full length, and had a zipper at the ankle so that you could easily get them on and off. The arm warmers were a standard length.

One feature I particularly liked was the silicone grippers at the top of the arm and leg warmers on both sides. That allowed them to grip my skin on one side to hold them in place, and then also grip the shorts or jersey on top of them. If you’ve ever had a bad set of arm or leg warmers that fall down, you’ll appreciate this feature.

Overall, the knee warmers and arm warmers have earned a place in my drawer. They do all the work of a regular arm or leg warmer, but have the added benefit of water repellency for when I get stuck out in cold, wet weather.

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I’d love to know in advance how to ‘fit’ leg warmers. I had a pair that slipped down constantly. I thought that was just how they worked, or at least how my legs were. A buddy also had a pair that slipped down. We agreed to swap them, the result: Both our ‘new’ pairs worked perfectly! No slippage now with my pair for over 2 years, in heavy rain even. So ‘fitting’ seems vital. Afraid I don’t really know how to predict this, but I’ll buy the same model again to make it work.

Great observation, Dave. I agree that when you find a brand and a size that works, it’s good to stick with it instead of, like me, ending up with a drawer full of L arm warmers that are long enough but don’t stay up on my cyclist arms, or Mediums that will stay up but don’t reach to my wrists.

I have owned these arm and leg warmers since they were introduced several years ago. They are fabulous and very aero. They are my goto arm warmers for time trials and duathlons on cold days. If I had run the Boston Marathon last Monday in the cold and wet, they would have been perfect!